The present invention is generally related to light sources, and more particularly to traffic signal lights including those incorporating both incandescent and solid state light sources.
Traffic signal lights have been around for years and are used to efficiently control traffic through intersections. While traffic signals have been around for years, improvements continue to be made in the areas of traffic signal light control algorithms, traffic volume detection, and emergency vehicle detection.
One of the current needs with respect to traffic signal lights is the ability to generate a homogenous light beam, that is, a light beam having a uniform intensity thereacross. Conventional incandescent lights tend to generate a light beam having a greater intensity at the center portion than the outer portions of the light beam. With respect to current solid state light sources, while LED arrays are now starting to be implemented, the light output of these devices can have non uniform beam intensities, due to optics and when one or more LEDs have failed.
There is desired an improved solid state light source generating a homogenous light beam therefrom.
The present invention achieves technical advantages as a solid state light source generating a homogenous light beam particularly useful in traffic control signals.
The solid state light source includes an area array of LEDs, a concave light diffuser having a convex lower surface facing the LED array, and a device interposed therebetween to uniformly direct light from the LED array to the convex bottom surface of the light diffuser. In one embodiment, an array of light guides are used to direct light from each LED to a respective portion of the light diffuser, each illuminated portion having the same surface area. The light guides toward the center of this light guide array are wider than the light guides communicating light from the outer LEDs due to the upwardly curved edge of the light diffuser. In the light guide embodiment, the light guide terminates proximate, but spaced from, the light diffuser to avoid a change in intensity of light at the interface between the light guides proximate the light diffuser.
In another embodiment, the LEDs are provided with lenses, whereby the lenses of the center LEDs have a smaller radius of curvature than the lenses over the outer LEDs which tend to be flatter and better columnate the light from the respective outer LEDs.